08Particle Background Scaling Up and Down by Simulated Distance

<main class="stage">
<div class="d3 is-demo" id="d3Root" tabindex="0">
  <canvas class="d3__canvas" id="d3Canvas" width="480" height="300"></canvas>
  <p class="d3__caption">Every particle's z value drifts slightly over time and is re-mapped to a screen size each frame, so an approaching particle keeps growing and a receding one keeps shrinking</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-paper);

.d3 {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-paper;
  outline: none;
}

.d3__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.d3__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 78%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .78);
  color: #fff;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .d3__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .d3 { cursor: default; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.d3 {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #ffffff;
  outline: none;
}

.d3__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.d3__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 78%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.78);
  color: #fff;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .d3__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .d3 {
    cursor: default;
  }
}

(function () {
  // 기법: 입자마다 zAdvanceSpeed 로 z값이 PARTICLE_Z_MAX 에서 0 쪽으로 시간에 따라 줄어들다가
  // 나머지 연산으로 다시 멀리 순환하고, sizeForDepth 가 그 z값을 매 프레임 화면 크기·화면 좌표로
  // 다시 환산한다 — 가까워질수록(z 작을수록) 입자가 커지고 화면 중심에서 바깥으로 퍼진다.
  var root = document.getElementById('d3Root');
  var canvas = document.getElementById('d3Canvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 160, CALC_H = 100;
  var CX = CALC_W * 0.5, CY = CALC_H * 0.5;
  var PARTICLE_Z_MAX = 120;
  var PARTICLE_COUNT = 34;
  var FOCAL = 60;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rnd = seedRand(429081);

  var particles = [];
  for (var i = 0; i < PARTICLE_COUNT; i += 1) {
    particles.push({
      worldX: (rnd() - 0.5) * 140,
      worldY: (rnd() - 0.5) * 90,
      zOffset: rnd() * PARTICLE_Z_MAX,
      speedScale: 0.6 + rnd() * 0.8,
      color: i % 3 === 0 ? '#6ec8ff' : (i % 3 === 1 ? '#b9a0ff' : '#4cd4a6')
    });
  }

  function zAdvanceSpeed(p) {
    return 0.012 * p.speedScale;
  }

  function zAt(p, t) {
    var raw = (p.zOffset - t * zAdvanceSpeed(p)) % PARTICLE_Z_MAX;
    if (raw < 0) raw += PARTICLE_Z_MAX;
    return raw + 1;
  }

  function sizeForDepth(z) {
    var v = (FOCAL / z) * 3.4;
    return Math.max(0.8, Math.min(7, v));
  }

  var elapsed = 0;
  var cw = 480, ch = 300;

  function drawScene(t) {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    ctx.clearRect(0, 0, cw, ch);

    for (var i = 0; i < particles.length; i += 1) {
      var p = particles[i];
      var z = zAt(p, t);
      var scale = FOCAL / z;
      var sizePx = sizeForDepth(z);
      var alpha = Math.max(0.18, Math.min(1, scale * 0.55));
      var dx = (CX + p.worldX * scale * 0.34) * sx;
      var dy = (CY + p.worldY * scale * 0.34) * sy;
      ctx.globalAlpha = alpha;
      ctx.fillStyle = p.color;
      ctx.beginPath();
      ctx.arc(dx, dy, sizePx * sx, 0, Math.PI * 2);
      ctx.fill();
    }
    ctx.globalAlpha = 1;
  }

  function fit() {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw; canvas.height = ch;
    drawScene(elapsed);
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reduce) root.classList.remove('is-demo');

  var warmSteps = reduce ? 0 : 130;
  for (var w = 0; w < warmSteps; w += 1) elapsed += 20;

  var lastTs = null;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var dt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!reduce) {
      elapsed += dt;
      drawScene(elapsed);
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  drawScene(elapsed);
  requestAnimationFrame(tick);
})();

import { useEffect, useRef } from "react";
import styles from "./Depth3dScaleDepthSizing.module.scss";

type Particle = {
  worldX: number;
  worldY: number;
  zOffset: number;
  speedScale: number;
  color: string;
};

export default function Depth3dScaleDepthSizing() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    if (!root || !canvas) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const wrap = canvas.parentElement as HTMLElement;

    const CALC_W = 160, CALC_H = 100;
    const CX = CALC_W * 0.5, CY = CALC_H * 0.5;
    const PARTICLE_Z_MAX = 120;
    const PARTICLE_COUNT = 34;
    const FOCAL = 60;

    function seedRand(seed: number) {
      let s = seed >>> 0;
      return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
    }
    const rnd = seedRand(429081);

    const particles: Particle[] = [];
    for (let i = 0; i < PARTICLE_COUNT; i += 1) {
      particles.push({
        worldX: (rnd() - 0.5) * 140,
        worldY: (rnd() - 0.5) * 90,
        zOffset: rnd() * PARTICLE_Z_MAX,
        speedScale: 0.6 + rnd() * 0.8,
        color: i % 3 === 0 ? "#6ec8ff" : (i % 3 === 1 ? "#b9a0ff" : "#4cd4a6")
      });
    }

    function zAdvanceSpeed(p: Particle) {
      return 0.012 * p.speedScale;
    }

    function zAt(p: Particle, t: number) {
      let raw = (p.zOffset - t * zAdvanceSpeed(p)) % PARTICLE_Z_MAX;
      if (raw < 0) raw += PARTICLE_Z_MAX;
      return raw + 1;
    }

    function sizeForDepth(z: number) {
      const v = (FOCAL / z) * 3.4;
      return Math.max(0.8, Math.min(7, v));
    }

    let elapsed = 0;
    let cw = 480, ch = 300;

    function drawScene(t: number) {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      ctx!.clearRect(0, 0, cw, ch);

      for (let i = 0; i < particles.length; i += 1) {
        const p = particles[i];
        const z = zAt(p, t);
        const scale = FOCAL / z;
        const sizePx = sizeForDepth(z);
        const alpha = Math.max(0.18, Math.min(1, scale * 0.55));
        const dx = (CX + p.worldX * scale * 0.34) * sx;
        const dy = (CY + p.worldY * scale * 0.34) * sy;
        ctx!.globalAlpha = alpha;
        ctx!.fillStyle = p.color;
        ctx!.beginPath();
        ctx!.arc(dx, dy, sizePx * sx, 0, Math.PI * 2);
        ctx!.fill();
      }
      ctx!.globalAlpha = 1;
    }

    function fit() {
      const r = wrap.getBoundingClientRect();
      cw = Math.max(1, Math.round(r.width));
      ch = Math.max(1, Math.round(r.height));
      canvas!.width = cw; canvas!.height = ch;
      drawScene(elapsed);
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (reduce) root.classList.remove("is-demo");

    const warmSteps = reduce ? 0 : 130;
    for (let w = 0; w < warmSteps; w += 1) elapsed += 20;

    let lastTs: number | null = null;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const dt = Math.min(ts - lastTs, 48);
      lastTs = ts;
      if (!reduce) {
        elapsed += dt;
        drawScene(elapsed);
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    drawScene(elapsed);
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.d3} is-demo`} ref={rootRef} tabIndex={0}>
        <canvas className={styles.d3__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.d3__caption}>입자마다 z값을 시간에 따라 조금씩 바꾸고 그 값을 화면 크기로 매 프레임 다시 환산해, 다가오는 입자는 점점 커지고 멀어지는 입자는 점점 작아진다</p>
      </div>
    </main>
  );
}